A reference point for a lot of information about Aperture is O'Reilly's Aperture Blog. You find most days at least two new entries tips, tricks and experiences around Aperture.
Related to O'Reilly's Aperture Blog is Aperture Plugged In with a presentation of plugins for Aperture. There are plugins for Flickr, istockphoto, Facebook etc. A lot of the plugins are for free, if you are using any of the related services. The webpage just received refreshed look, which makes it easier to navigate and find relevant information and there is so much more to explore.
Another resource that I just found today via Aperture Plugged In, is Aperture Users Professional Network. This page appears to be resourceful as well. You need to sign up in order to be able to read some of the more in depth articles etc. There is a free membership (for which I opted, at least for now) and a paid membership. They organise course and tutorials, which you can attend as well.
If you have any other good links about Aperture, please let me know, so that I can upload them here.